2. Evolution of tempering softening on carbonitrided unalloyed steel

In order to limit the interaction of absorbed nitrogen with the additive elements, it is preferable to concentrate on an unalloyed steel (C10) and to study the evolution of the hardness profile after holding for 2 h at 150°C and 250°C on a carbonitrided sample (carbo HN ⁺ type). It is important to bear in mind that a steel containing 0.1% C, even if surface case-hardened to 0.8% C, will not achieve a hardness of 500 HV0.5 after oil quenching in an industrial charge, given its low hardenability. The results shown in figure 3 provide an initial indication of the powerful effect of nitrogen on the hardenability of this type of steel. Moreover, it is interesting to note that the hardness recorded at a depth of 100...